Interferons are proteins with a molecular weight of between 15 and 30 kD, and present great problems of storage owing to their instability. Numerous proposals have been made in the literature for stabilizing interferon-containing preparations, for example using human serum albumin, glucose, mannitol and a number of other compounds as stabilizers. Alpha-interferons have also been proposed for use in the treatment of viral diseases in the eye; however, it is particularly difficult to produce ointments or drops which will retain their activity for shelf storage.
Japanese Kokai Tokyo Koho J. P. No. 55/102519 (80 102.519) describes a method of stabilizing interferon by freeze-drying in the presence of Tris(hydroxymethylamino)-methane, a non-ionic polyethylene surfactant and an antibiotic. It was reported in U.S. Pat. No. 4,252,791 that lanthanides and calcium salts increase the mechanical and thermal stability of interferons. It is known from European Patent Application No. 82.481 that amino acids (e.g. glycine and alanine) stabilize buffered (pH 7.0-7.4) lyophilized interferon. According to Sedmak, J.J., et. al. (Adv. Exp. Med. Biol. 1978, 110), human fibroblast interferon at low pH values is only stable in the presence of more than 5 mcg/ml of protein, and mechanical stress has an inactivating effect on the interferon. It can be said that interferons in general, and alpha-2-interferon in particular, very rapidly lose their activity in aqueous solution without any stabilizers and even pure interferon lyophilizates prepared by freeze-drying acidic aqueous solutions are only relatively stable on storage if stabilizers such as human serum albumin and optionally buffer substances such as ammonium acetate buffer are added to them.